Latent infection with feline syncytial virus of cell cultures prepared from the kidneys of new-born kittens.

Feline syncytial virus infection was detected in 4 out of 30 secondary or tertiary cultures of kidney cells from new-born kittens. Such infection was not detected in any primary cell culture. The syncytia-forming virus was readily transmissible by infected cells. One strain was transmissible to heterologous (bovine and canine) secondary cells, but did not infect MDBK and PK-15 cell lines. Based on biochemical, untrastructural and serological characteristics, the virus was designated a member of the subfamily Spumavirinae of the family Retroviridae. As endogenous infection of primary cell cultures may not be detectable by cytopathic effect, it is suggested that only well-controlled secondary cat cells or cell lines should be used in work with feline viruses.